• Journal of the Korea Computer Graphics Society
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• v.4 no.1
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• pp.79-88
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• 1998

Till now there are several rendering models for water and simulating other fluids and their dynamics. Especially in order to generate a curved surface of flexible objects such as liquid and snow, the implicit metaball formulation is widely used in favor of its simplicity and flexibility. This paper proposes one excellent method for generating water droplets, which would be deformed in gravitation field. In previous works, a water droplet was simply represented by approximated curved surfaces of a symmetric metaball. Thus the final result of the rendered water droplet was far from a realistic droplet, because they do not consider the gravitational effect in droplets. We propose a new metaball model for rendering water droplets placed on an arbitrary surface considering the gravitation and friction between droplet and plate. Our new metaball model uses a new vector field isosurface function to control the basic scalar metaball with respect to the norm of gravitational force. In several experiments, we could render a photo-realistic water droplets with natural-looking shadows by applying ray-tracing.

• Journal of the Korea Computer Graphics Society
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• v.14 no.1
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• pp.1-10
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• 2008

In this paper, we present a novel method for creating a hand-painted painterly animation, starting from a video input. One of the most important aspects in painterly animation is to maintain the temporal coherence of brush strokes between frames, which plays a vital role to warrant a smooth transition between frames. Our unique utilization of motion areas enables users to produce a smooth movement of brush strokes. The motion areas are the parts where objects move between frames and they are categorized in two main types. A strong motion area is the part where the movement of real edges and hidden edges is determined by the motion vector between frames. The real edge is the outline of an object and the hidden edge is the boundary to represent the direction of a grain of intensity in the areas with gradations. A weak motion area is the remainder after subtracting the strong motion area from the entire motion area. Temporally coherent painterly animation is achieved by re-painting the brush strokes on the canvas using two motion areas, resulting in a natural and hand-painted appearance.

• Journal of the Korea Computer Graphics Society
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• v.24 no.4
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• pp.21-27
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• 2018

In this paper, we propose a real-time interaction method using user's mouth wind in mobile device. In mobile and virtual reality, user interaction technology is important, but various user interface methods is still lacking. Most of the interaction technologies are hand touch screen touch or motion recognition. In this study, we propose an interface technology that can interact with real time using user's mouth wind. The direction of the wind is determined by using the angle and the position between the user and the mobile device, and the size of the wind is calculated by using the magnitude of user's mouth wind. To show the superiority of the proposed technique, we show the result of visualizing the flow of the vector field in real time by integrating the mouth-wind interface into the Navier-Stokes equations. We show the results of the paper on mobile devices, but can be applied in the Agumented reality(AR) and Virtual reality(VR) fields requiring interface technology.

• Journal of the Korea Computer Graphics Society
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• v.6 no.4
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• pp.35-42
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• 2000

3D texture mapping generates highly natural visual effects in which objects appear carved from lumps of materials rather than laminated with thin sheets as in 2D texture mapping. Storing 3D texture images in a table for fast mapping computations, instead of evaluating procedures on the fly, however, has been considered impractical due to the extremely high memory requirement. Recently, a practical real-time 3D texture mapping technique was proposed in [11], where they attempt to resolve the potential texture memory problem by compressing 3D textures using a wavelet-based encoding method. In this paper, we consider two other encoding schemes that could also be applied to the compression-based 3D texture mapping. In particular, we extend the vector quantization and FXT1 for 3D texture compression, and compare their performance with the wavelet-based encoding scheme.

• Journal of KIISE:Computer Systems and Theory
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• v.32 no.11_12
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• pp.692-704
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• 2005

With the improvement of computer hardware, GPUs(Graphics Processor Units) have tremendous memory bandwidth and computation power. This leads GPUs to use in general purpose computation. Especially, GPU implementation of compute-intensive physics based simulations is actively studied. In the solution of differential equations which are base of physics simulations, tridiagonal matrix systems occur repeatedly by finite-difference approximation. From the point of view of physics based simulations, fast solution of tridiagonal matrix system is important research field. We propose a fast GPU implementation for the solution of tridiagonal matrix systems. In this paper, we implement the cyclic reduction(also known as odd-even reduction) algorithm which is a popular choice for vector processors. We obtained a considerable performance improvement for solving tridiagonal matrix systems over Thomas method and conjugate gradient method. Thomas method is well known as a method for solving tridiagonal matrix systems on CPU and conjugate gradient method has shown good results on GPU. We experimented our proposed method by applying it to heat conduction, advection-diffusion, and shallow water simulations. The results of these simulations have shown a remarkable performance of over 35 frame-per-second on the 1024x1024 grid.

• Journal of KIISE:Computer Systems and Theory
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• v.37 no.3
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• pp.184-193
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• 2010

This paper proposes a biological iridescence BRDF(Bidirectional Reflectance Distribution Function) compression and rendering method. In the graphics technology, iridescence sometimes is named structure colors. The main features of these symptoms are shown transform of color and brightness by varying viewpoint. Graphics technology to render this is the BRDF technology. The BRDF methods enable realistic representation of varying view direction, but it requires a lot of computing power because of large data. In this paper, we obtain reflection map from iridescence BRDF, analyze color of reflection map and propose representation method by several colorfully concentric circle. The one concentric circle represents beam width of reflection ray by one normal vector. In this paper, we synthesize rough concentric by using several virtually optical normal vectors. And we obtain spectrum information from concentric circles passing through the center point. The proposed method enables IBR(image based rendering) technique which results is realistic illuminance and spectrum distribution by one texture from reduced BRDF data within spectrum.

• The KIPS Transactions:PartA
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• v.14A no.4
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• pp.191-196
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• 2007

In the field of computer graphics, Navier-Stokes equations would be used for realistic simulations of smokes and currents. However, implementations derived from these equations are hard to achieve for real-time simulations, mainly due to its massive and complex calculations. Thus, there have been various attempts to approximate these equations for real-time simulation of smokes and others. When the advection terms of the equations are approximated by the Semi-Lagrange methods, the fluid density can be rapidly reduced and small-scale vorticity phenomena are easy to be missed, mainly due to the numerical losses over time. In this paper, we propose an improved numerical method to approximately calculate the advection terms, and thus eliminate these problems. To calculate the advection terms, our method starts to set critical regions around the target grid points. Then, among the grid points in a specific critical region, we search for a grid point which will be advected to the target grid point, and use the velocity of this grid point as its advection vector. This method would reduce the numerical losses in the calculation of densities and vorticity phenomena, and finally can implement more realistic smoke simulations. We also improve the overall efficiency of vector calculations and related operations through GPU-based implementation techniques, and thus finally achieve the real-time simulation.

• Journal of Digital Convergence
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• v.15 no.12
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• pp.495-502
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• 2017

Modern ceramics is exploring the expansion of the area with various expression techniques. The silhouette technique among various expressive decoration techniques is a representative expression technique of object form expression. This emphasizes the outline of the form and expresses it and omits the inner form. It gives simplicity and intensity, and awakens aesthetic sensibility and imagination. Therefore, the researcher designed the material related to the core image of the story by designing it as a silhouette technique by using the "Acorn Story" as a subject and then making the transfer paper by using the vector graphic. The transferred paper was expressed on a ceramic plate by transferring technique. Therefore, I hope that this research, beyond the merely decorative function of ceramic expression, will become a ceramic design that will awaken imagination and aesthetic sensibility in digital information age.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.1
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• pp.1-12
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• 2008

In this paper, we present a real-time algorithm for recognizing the vehicle color from the indoor and outdoor vehicle images based on GPU (Graphics Processing Unit) acceleration. In the preprocessing step, we construct feature victors from the sample vehicle images with different colors. Then, we combine the feature vectors for each color and store them as a reference texture that would be used in the GPU. Given an input vehicle image, the CPU constructs its feature Hector, and then the GPU compares it with the sample feature vectors in the reference texture. The similarities between the input feature vector and the sample feature vectors for each color are measured, and then the result is transferred to the CPU to recognize the vehicle color. The output colors are categorized into seven colors that include three achromatic colors: black, silver, and white and four chromatic colors: red, yellow, blue, and green. We construct feature vectors by using the histograms which consist of hue-saturation pairs and hue-intensity pairs. The weight factor is given to the saturation values. Our algorithm shows 94.67% of successful color recognition rate, by using a large number of sample images captured in various environments, by generating feature vectors that distinguish different colors, and by utilizing an appropriate likelihood function. We also accelerate the speed of color recognition by utilizing the parallel computation functionality in the GPU. In the experiments, we constructed a reference texture from 7,168 sample images, where 1,024 images were used for each color. The average time for generating a feature vector is 0.509ms for the $150{\times}113$ resolution image. After the feature vector is constructed, the execution time for GPU-based color recognition is 2.316ms in average, and this is 5.47 times faster than the case when the algorithm is executed in the CPU. Our experiments were limited to the vehicle images only, but our algorithm can be extended to the input images of the general objects.

• The Transactions of the Korea Information Processing Society
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• v.2 no.1
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• pp.130-136
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• 1995

This paper is on the development of tools to generate pointillist representation-like images automatically by computer. Pointillist representation -like effects on the generated images are enforced by steps as follows. First, the position of brush stroke is determined from the gradient vector so that the brush touches look more natural. Second, pointillist representation-like coloring is endorsed by changing saturation and value using the RGB components of image. Our approach combines image processing techniques with computer graphics techniques for more faithful pointillist representation-like images and a couple of sample images are presented to show the effectiveness.